Zebrafish (Danio rerio) are small freshwater fish of the family Cyprinidae whose adult length is about 4 to 5 cm. Zebrafish are easy to breed, fertile, and short in generation time, which are characteristics suitable for genetics studies. Furthermore, zebrafish are easy to be genetically manipulated and functionally analyzed. In addition, many of the development and organogenesis mechanisms of zebrafish have high commonality with those of higher vertebrates including human beings. Zebrafish are therefore widely used as experimental animals (model animals) in the fields of medical science, physiology, biological science, and the like.
Zebrafish, which are model animals, live in groups. Thus, in a case of research using zebrafish as model animals, identification of individual zebrafish living in groups is required for improvement of research accuracy.
A typical method for identifying animals individually is to implant or attach a label such as a marker or a microchip in the body or onto the body surface of each animal. However, the small size of zebrafish makes implanting or attaching a label in or onto them difficult. Even if labels could be implanted or attached, the labels would likely detach while the zebrafish are swimming. Furthermore, invasively implanting or attaching a label does great damage to the fish body. In addition, a device for detecting the labels would be required, and the operation for detecting the labels would be cumbersome.
A need has therefore been felt for a method for non-invasively, simply and reliably identifying individual when zebrafish are used as model animals.